I haven’t personally tried them, but there are a lot of monitors on Amazon that are meant for Raspberry-Pi’s. I was looking at them myself but I instead decided to get an old monitor for free off of Freecycle. I made a post there and a bunch of people offered a bunch of old ones they weren’t using any more (like the ubiquitous Samsung 720N).
Also, I already have a second monitor but it’s too narrow for discord; as in the window can’t be made small enough. Maybe it’s just a GNOME thing, but I’m not sure discord will ‘fit’ on those small screens.